Ink-jet head

ABSTRACT

An ink-jet head to jet ink from a front side thereof includes an actuator in which a plurality of parallel channels for generating pressure change to be applied to ink are formed and having a nozzle surface on which a plurality of nozzle holes are formed to jet ink from a corresponding ink channel, and a front plate located at the front side of the nozzle surface so as to protect the nozzle surface and having a recessed section on a front surface of the front plate, wherein the recessed section has an opening in which the nozzle surface of the actuator is inserted in such a way that the nozzle surface is located between the front surface of the front plate and the bottom surface of the recessed section.

FIELD OF THE INVENTION

The present invention relates to an ink-jet head for recording a desiredimage by jetting ink from nozzles onto a recording medium, wherein afront plate of the ink-jet head is improved. The front plate is appliedto the surface of a nozzle plate to serve as a flat plate for protectionof the nozzle surface, prevention of peeling of the nozzle plate, andproviding a plane to have tight contact with a suction cap for suckingink from the nozzles.

BACKGROUND OF THE INVENTION

An ink-jet head for recording a desired image by jetting ink fromnozzles onto a recording medium is maintained, to be able to jet ink ina normal state all the time, in such a manner that: ink is periodicallyand forcibly subjected to suction from nozzles; thus high viscosity inkaccumulated in nozzles is exhausted; and thereby blockage in nozzles isresolved.

To suck ink as described above, it is necessary to cause a suction capto tightly contact with the nozzle surface of the ink-jet head. However,the nozzle plate of an ink-jet head is extremely small, and even anozzle plate having several hundreds of nozzles has dimensions, forexample, 1 cm multiplied by several cm, or the like. Accordingly, whenink is sucked from nozzles, there are problems in that the nozzlescannot be covered with a suction cap enough, that, even when the nozzlesare covered with the suction cap, the suction cap does not contact withthe nozzles tight enough to ensure airtight, and so on. Further,although the nozzle plate is bonded to the front end of an actuator, thegap between the nozzle plate and the recording medium is so small asapproximately 1 mm. Therefore, if the recording medium has come incontact with the ink-jet-head, a paper jam may occur on the recordingmedium and a large force may be applied to the head, which peels thenozzle plate off the actuator. Therefore, with respect to an ink-jethead, enclosing the periphery of a nozzle plate by a front plate iscarried out to prevent these problems.

Thus, an ink-jet head is arranged in such a way that a nozzle surface islocated in an opening of a front plate formed in a flat plate shapehaving the opening. By this front plate, the surface of a nozzle plateis protected; peeling of the nozzle plate is protected; and a spacelarge enough to allow tight contact of a suction cap with the nozzleplate is formed.

However, if the front plate encloses the nozzle plate, ink gathers atthe joint edge between the nozzle plate and the front plate. In thissituation, although ink on the nozzle surface of the ink-jet head can beremoved by wiping with a blade, the nozzle surface is desirably arrangedat a position, in the opening of the front plate, deeper than theposition of the surface of the front plate in order to prevent damage ofnozzles due to, for example, rubbing with the recording medium. However,if nozzle surface 100 a is arranged in a deeper position (the lower sidein the figure) in opening 111 than surface 110 a of front plate 110, ink200 and dust easily gather at the joint edge between nozzle plate 100and the front plate 110. Accordingly, wiping of the nozzle surface 100 acannot be performed effectively. Further, if the ink 200 having gatheredhere touches with a nozzle 101, problems such as disturbance of inkjetting and the like occur.

On the other hand, as shown in FIG. 6, if the nozzle surface 100 a isarranged protruding from the surface 110 a of the front plate 110, evenwhen ink 200 or dusts gather at the joint edge between the nozzle plate100 and the front plate 110, since the ink 200 or the dusts do not comein contact with the nozzle 101, ink jetting cannot be disturbed.However, since the nozzle surface 100 a is protruding from the surface110 a of the front plate 110, the nozzle surface 100 a cannot beprotected, which causes problems of scratching the water repellentsurface and peeling the nozzle plate 100.

For example, Patent Document 1, described later, discloses a technologyin which a head cap for protection of a nozzle plate is arrangedenclosing the nozzle plate, the nozzle surface is positioned 2 to 20 μmdeeper than the surface of the head cap so that a blade and a recordingmedium do not come in hard contact with the nozzle surface, and thus awater repellent film coated on the nozzle surface can be prevented frompeeling.

Further, Patent Document 2, described later, discloses a technology inwhich a nozzle plate cover is arranged around the periphery of a nozzleplate, the nozzle surface is positioned protruding toward a recordingmedium from the nozzle plate cover by the height not greater than thethickness of the plate, and thus the nozzle plate is prevented frompeeling.

Still further, Patent Document 3, described later, discloses atechnology in which, as shown in FIG. 7, in the state that nozzlesurface 100 a is protruded from surface 110 a of front plate 110,adhesive 300 is applied to the edge space therebetween, then, anactuator is drawn back to move the nozzle surface 100 a to a deeperposition than the surface 110 a of the front plate 110, and in thisstate, the adhesive 300 is cured. Thus, the step generated between thenozzle surface 100 a and opening 111 of the front plate 110 is smoothedby the adhesive 300 to reduce ink that remains after cleaning by ablade.

-   -   (Patent Document 1) TOKKAI No. 2000-141652    -   (Patent Document 2) TOKKAI No. 2001-150668    -   (Patent Document 3) Patent No. 3127573

In the technology disclosed in Patent Document 1, as the nozzle surfaceis drawn to a position a little deeper than the surface of the frontplate, the nozzle surface is protected. However, as a step is generatedbetween the nozzle surface and the surface of the front plate, whenremoving ink adhering to the nozzle surface by wiping, ink tends togather in the step, which may cause ink jetting failure due to thecontact of the gathering ink with nozzles.

In the technology disclosed in Patent Document 2, although ink does notgather on the nozzle surface since the nozzle surface is protruded alittle from the surface of the front plate, the nozzle surface cannot beprotected enough.

In the technology disclosed in Patent Document 3, there is a problemthat adhesive tends to flow into nozzles. To prevent this flow in of theadhesive, painstaking mask treatment is required, and further, to stablyform the shape of the adhesive, it is necessary to finely control therelative position between the nozzle surface and the front plate afterapplying the adhesive, according to various conditions including thecharacteristics of the adhesive, the environmental temperature, and thedimensions of the gap between the nozzle surface and the opening of thefront plate, which causes a problem of extreme difficulty in control ofthe adhesive and the shape thereof.

The defect common to the above technologies is that it is impossible toprevent ink from gathering at the joint edge between an actuator and afront plate, because an opening having a rectangular cross-section withdimensions which the actuator just fits in is formed through the frontplate, and the actuator is inserted in the opening.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an ink-jet head, with asimple structure, that solves the conflict between-requirement forprotection of a nozzle surface and prevention of peeling of the nozzleplate, and requirement for maintainability of the nozzle surface.

To solve the problems described above, in the first aspect of theinvention, there is provided an ink-jet head comprising: a plurality ofparallel channels for generating pressure change to be applied to ink,an actuator provided with a number of disposed nozzles for jetting inkin each channel to a nozzle surface, and a front plate having an openingthat encloses the nozzle surface, wherein a recessed section is providedon the surface of the front plate; the opening is formed in the centralpart of the bottom of the recessed section; further, the actuator isinserted in the opening; and the position of the nozzle surface is onthe bottom side of the recessed section with respect to the surface ofthe front plate and on the front plate surface side of the recessedsection with respect to the bottom of the recessed section.

According to the invention, since the position of the nozzle surface ison the bottom side of the recessed section with respect to the surfaceof the front plate, a recording medium or a blade does not come in hardcontact with the nozzle surface. Therefore, a water repellent filmcannot be scratched easily, and peeling of the nozzle plate can beprevented.

Further, as the location of the nozzle surface is on the front platesurface side of the recessed section with respect to the bottom of therecessed section, even if ink gathers on the step at the joint edgebetween the actuator and the front plate, ink is prevented from flowinginto nozzles.

Still further, as the blade enters the opening, ink adhering to thenozzle surface can be easily wiped.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external isometric view of an ink-jet head in accordancewith the present invention;

FIG. 2 is a cross-sectional view principally showing a schematicstructure of an actuator;

FIG. 3 is a cross-sectional view showing a relationship between a nozzlesurface of the actuator and an opening of a front plate;

FIG. 4 is a cross-sectional view showing another embodiment of therelationship between a nozzle surface of an actuator and an opening of afront plate;

FIG. 5 is a diagram explaining a conventional relationship between anozzle surface of an actuator and an opening of a front plate;

FIG. 6 is a diagram explaining another conventional relationship betweena nozzle surface of an actuator and an opening of a front plate; and

FIG. 7 is a diagram explaining a manufacturing method of a conventionalink-jet head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is an external isometric view of an ink-jet head in accordancewith the present invention, and FIG. 2 is a cross-sectional viewprincipally showing the schematic structure of an actuator.

In FIG. 1, symbol A denotes the ink-jet head, and numeral 1 denotes theactuator. On the front face of the actuator 1, nozzle plate 11 providedwith a number of disposed nozzles 11 a for jetting ink is adhered. Theactuator 1 comprises a non-piezoelectric ceramic substrate having alongitudinal shape and a number of parallel channels corresponding tothe respective nozzles 11 a, and a ceramic member that is arranged onthe non-piezoelectric ceramic substrate and provided with piezoelectricceramic layers having opposite polarization directions. The actuator 1generates pressure change to be applied to ink.

Each channel 12 is formed by cutting the non-piezoelectric ceramic in alinear thin channel shape by a diamond blade or the like, wherein theremaining non-piezoelectric ceramic forms isolation walls 13 betweenrespective channels 12, 12 neighboring to each other. The depth of eachchannel 12 gradually becomes smaller as it comes closer to the right endin the figure, and finally becomes zero. On a part of the surface ofeach channel 12, a metal electrode (not shown) is formed.

Further, from above the channels 12, a cover substrate 14 of anon-piezoelectric ceramic substrate, or the like, is adhered. Throughthe cover substrate 14, opening 14 a led to all the channels 12 isformed at the position corresponding to the shallow portions of thechannels 12. To cover the opening 14 a, manifold 15 is arranged, andthus, shared ink chamber 16 is formed between the inner surface of themanifold 15 and the shallow portions of the respective channels 12 todistribute ink to the respective channels 12.

As the material of the non-piezoelectric ceramic substrate, at least oneof aluminum, aluminum nitride, zirconia, silicon, silicon nitride,silicon carbide, crystal is preferably employed so that polarizedpiezoelectric ceramic is securely supported even if the isolation walls13 are subjected to shear-deformation.

As the material of the piezoelectric ceramic, ceramic, such as PZT orPLZT, which is a mixed crystallite mainly of PbOx, ZrOx, TiOx,containing a trace amount of a metallic oxide known as a softening agentor a hardening agent, such as Nb, Mg, Sn, Ni, La, Cr, etc. is preferablyemployed.

PZT is lead titanate zirconate having a large filling density, a largepiezoelectric constant, and an excellent processability. Therefore, PZTis a preferable material. If the temperature of PZT is dropped afterburning, the crystallographic structure suddenly changes, atoms aredeviated, and the PZT turns into an aggregate of minute crystals in aform of a dipole of which one side is positive and the other side isnegative. Such a spontaneous polarization has random direction, cancelsthe polarities to each other, and therefore needs further polarizationtreatment.

In polarization treatment, a thin plate of PZT is sandwiched byelectrodes, immersed into silicon oil, subjected to a high electricfield of approximately 10 to 35 kv/cm, and thus polarized. When avoltage is applied to the polarized PZT orthogonally to the polarizationdirection, the side walls are shear-deformed into a dogleg shape in anoblique direction due to piezoelectric effect, and thus the volume ofthe ink chamber expands.

As the material of the metallic electrodes, gold, silver, aluminum,palladium, nickel, tantalum, or titanium can be employed, andparticularly, gold and aluminum are preferable due to electriccharacteristics and processability, wherein the electrodes are formed byplating, vapor deposition, and sputtering. Each metallic electrode isdrawn out from inside each channel 12, through a shallow recessedsection portion, up to the top face on the rear side (right end in FIG.2) of the actuator 1, and electrically connected by a signal cable (notshown) with a drive circuit.

The nozzle plate 11 is formed of plastic such as, polyalkyleneterephthalate, polyimide, polyetherimide, polyetherketone,polyethersulfone, polycarbonate, cellulose acetate, etc., and thesurface of the this nozzle plate 11 (the surface on the side where inkis jetted from nozzles 11 a) is the nozzle surface 1 a.

With respect to the actuator 1 arranged as above, when a drive voltagegiven by a drive circuit is applied to the electrodes in the respectivechannels 12, the isolation walls 13 are shear-deformed to generate apressure change in the channels 12, and then ink, in the channels 12,subjected to a pressure is jetted from the nozzles 11 a. The ink havingbeen jetted flies forward in the longitudinal direction of the channels12 and impacts a recording medium such as paper.

As shown in FIG. 1, the actuator 1 is housed in housing 2, and withrespect to the housing 2, the front plate 3 is provided on the same sideas the nozzle surface 1 a of the actuator 1.

The front plate 3 is made of, for example, acryl, polycarbonate,polyetherimide, modified PPE, aluminum, stainless steel, etc., andalmost in the central part of the front plate 3, opening 31 almost inthe same shape as the nozzle surface 1 a of the actuator 1 is provided.The actuator 1 is inserted in the opening 31 so that the nozzle surface1 a of the actuator 1 is positioned to face outside from the opening 31.

Therefore, with respect to this ink-jet head A, a wide flat plate shapedspace is formed by the front plate 3 around the nozzle surface 1 a ofthe actuator 1. When ink is forcibly sucked from the nozzles 11 a of theactuator 1 by the use of a suction cap (not shown), the ink can besucked by having the suction cap tightly contact with the surface 3 a ofthe front plate 3, wherein the suction cap covers the nozzle surface 1 aof the actuator 1.

Further, the nozzle surface 1 a of the actuator 1 and the opening 31 ofthe front plate 3 are shown in FIG. 3 in detail.

As shown in the figure, the front plate 3 is greater than the nozzlesurface 1 a of the actuator 1, and formed with recessed section 32hollowed from the surface 3 a of the front plate 3. In the central partof the recessed section 32, the above opening 31 is formed.

In the opening 31 of the front plate 3, the position of the nozzlesurface 1 a of the actuator 1 is located on the bottom 32 a side of therecessed section 32, which is on the deep side (lower side in FIG. 3),with respect to the surface 3 a of the front plate 3, and on the frontplate surface 3 a side (upper side in FIG. 3) of the recessed section 32with respect to the bottom 32 a of the recessed section 32. Therefore,the surface 3 a of the front plate 3 is stepped to the deep side fromthe nozzle surface 1 a only in the periphery of the nozzle surface 1 a,wherein the actuator 1 is adhered to the opening 31 of the front plate 3by the use of adhesive.

As described above, since the nozzle surface 1 a is stepped deeper thanthe surface 3 a of the front plate 3, even when a recording medium comesinto contact with the front plate 3, it does not come into directcontact with the nozzle surface 1 a. Therefore, a water repellent filmcoated on the nozzle surface 1 a is prevented from damage, and thenozzle plate 11 cannot be peeled.

Further, in performing maintenance work, even when ink remaining afterwinding by a blade gathers in the bottom 32 a of the recessed section 32of the front plate 3, as the nozzle surface 1 a is protruding from thebottom 32 a of the recessed section 32 toward the surface 3 a of thefront plate 3, this ink does not come in contact with the nozzle surface1 a, and accordingly, the ink does not come in contact with nozzles,avoiding prevention of ink jetting.

Further, as the step of the recessed section 32 has room to let a bladeenter during wiping, ink having gathered here can be easily wiped andremoved.

As shown in FIG. 3, representing the distance between the surface 3 a ofthe front plate 3 and the nozzle surface 1 a of the actuator 1 by d1,the distance between the nozzle surface 1 a of the actuator 1 and thebottom 32 a of the recessed section 32 by d2, and the width of thebottom 32 a of the recessed section 32 by d3, the above described d1 ispreferably set in the range 0<d1≦(d3)/2. If d1 is greater than (d3)/2,the depth from the surface 3 a of the front plate 3 is too large, and itis difficult for the tip end of a blade to reach the nozzle surface 1 ain winding the nozzle surface 1 a by the blade. Thus, the problems ofunevenness of wiping and remains after wiping are caused, degrading themaintainability.

Further, the above d2 is preferably set in the range 0<d2≦0.5 mm. If d2is greater than 0.5 mm, the amount of remaining ink in the recessedsection 32 becomes too large when performing suction of ink, and also,it becomes difficult to wipe the remaining ink by a blade.

Still further, the above d3 is preferably set in the range 0.1<d3≦2 mm.If d3 is smaller than 0.1 mm, when wiping the nozzle surface 1 a by theblade, it is difficult for the tip end of the blade to reach the nozzlesurface 1 a, causing unevenness of wiping and remains after wiping todegrade maintainability, and also, if ink or dust remains between anedge of the nozzle surface 1 a and the recessed section 32 after havingperformed wiping the nozzle surface 1 a by the blade, it is difficult tokeep the ink or the dust in the recessed section 32, thereby causing thepossibility of contaminating again the nozzle surface 1 a. On the otherhand, if d3 is larger than 2 mm, the protection function by the surface3 a of the front plate 3 degrades, and it is possible that, when arecording medium moves up, the recording medium rubs the nozzle surface1 a. Further, the head suction cap becomes larger.

When d1, d2, and d3 respectively satisfy the above ranges, protection ofthe nozzle surface 1 a by the surface 3 a of the front plate 3,prevention of peeling of the nozzle plate 11, and maintainability inwiping the nozzle surface 1 a by the blade, can be best satisfied. Morepreferably, d1, d2, and d3 are set in the respective ranges 0.05mm≦d1≦(d3)/3 for d1, 0.05 mm≦d2≦0.2 mm for d2, and 0.2 mm≦d3≦1 mm ford3.

As a method for forming the recessed section 32, as stated above, in theperiphery of the opening 31 of the front plate 3, processing of forminga resin die, aluminum die cast processing, and metal press processingcan be employed, according to the material. In this way, as the recessedsection 32 can be formed by mechanical processing on the front plate 3,it is allowed to form the recessed section 32 into a stable shape andwith easiness.

Although, in FIG. 3, the shape of the bottom 32 a of the recessedsection 32 forms a plane which is almost parallel to the surface 3 a ofthe front plate 3 and the nozzle surface 1 a of the actuator 1, there isno limitation to this. The cross-section of the bottom 32 a of therecessed section 32 may be a concave shape hollowing into the deep side(lower side in FIG. 3) in an arc shape, or as shown in FIG. 4, it isalso allowed to form slope surface 32 b by which the inner peripheraledge of the opening 31 of the front plate 3 and the outer peripheraledge (boundary with the surface 3 a) of the recessed section 32 aresmoothly and continuously connected.

1. An ink-jet head to jet ink from a front side thereof, comprising: anactuator in which a plurality of parallel channels for generatingpressure change to be applied to ink are formed and having a nozzlesurface on which a plurality of nozzle holes are formed to jet ink froma corresponding ink channel; and a front plate located at the front sideof the nozzle surface so as to protect the nozzle surface and having arecessed section on a front surface of the front plate, wherein therecessed section has an opening in which the nozzle surface of theactuator is inserted in such a way that the nozzle surface is locatedbetween the front surface of the front plate and the bottom surface ofthe recessed section.
 2. The ink-jet head of claim 1, wherein thefollowing formula is satisfied:0 mm<d1≦(d3)/2 where d1 represents a distance between the front surfaceof the front plate and the nozzle surface and d3 represents a distancebetween a side of the recessed section and a side of the nozzle surface.3. The ink-jet head of claim 1, wherein the following formula issatisfied:0<d2≦0.5 mm where d2 represents a distance between the nozzle surfaceand the bottom surface of the recessed section.
 4. The ink-jet head ofclaim 1, wherein the following formula is satisfied:0.1≦d3≦2 mm where d3 represents a distance between a side of therecessed section and a side of the nozzle surface.
 5. The ink-jet headof claim 1, wherein the following formulas are satisfied:0.05 mm≦d1≦(d3)/3;0.05≦d2≦0.2 mm; and0.2≦d3≦1 mm where d1 represents a distance between the front surface ofthe front plate and the nozzle surface; d2 represents a distance betweenthe nozzle surface and the bottom surface of the recessed section; andd3 represents a distance between a side of the recessed section and aside of the nozzle surface.
 6. The ink-jet head of claim 1, wherein alateral cross-section of the recessed section is an arc shape thathollows into a deep side of the front plate from the front surface ofthe front plate.
 7. The ink-jet head of claim 1, wherein a slope surfaceby which an inner peripheral edge of the opening of the recessed sectionand an outer peripheral edge of the recessed section are smoothly andcontinuously connected is formed instead of forming the bottom surfaceof the recessed section.
 8. The ink-jet head of claim 1, wherein a waterrepellent film is coated both on the nozzle surface and the bottomsurface of the recessed section.
 9. The ink-jet head of claim 7, whereina water repellent film is coated both on the nozzle surface and theslope surface of the recessed section.